Students must gear their NXT car to complete the course the fastest. The course consists of a flat section and an inclined section.

Lesson Objectives:

To learn about gear ratios, gearing for torque vs gearing for speed, optimization, and building.

Materials Needed:

NXT kit

Ramp

Computers running MINDSTORMS

Preparation and Set Up:

Prepare one or more courses – With a flat beginning and an incline ending. The length of both sections will determine the optimum gear ratio. To allow for extensions, set up other courses with varying distances of the course components.

Necessary Background

Using gear ratios students can gear their cars for more torque or more speed. If the drive gear is bigger than the driven gear, the car will be geared for speed. If the other way around, it will be geared for torque.

A car geared for torque will be slower, but will climb better. A car geared for speed will be quick, but might not be able to climb the ramp.

Vocabulary:

Gear Ratio – The ratio of the speed of rotation of the drive gear of a gear train to that of the driven gear.

Drive Gear- The gear attached to the source of torque. (Usually the motor).

Driven Gear – The gear that receives motion from the drive gear.

Optimization – Finding a balance between design concerns that yields the best solution.

Procedure

Introduction – 10 Minutes Ask students if they’ve ever used gears before. More than likely, they’ve driven a 10 speed bike before, and never knew how the gears worked. Introduce students to gears and gear ratios. Using a pre-made gear train, show them the size of the drive gear and the driven gear, and ask if the driven gear will spin faster or slower than the drive. If they are having trouble seeing it, ask them for every one rotation of the drive gear, how many times does the driven gear rotate? Explain torque vs. speed. ie. tugboats – high torque, low speed. Handheld fans- high speed, low torque. Introduce the concept of optimization. Introduce the activity Activity – 40 minutesClean up/ Wrap up – 10 minutes

What was easiest? What was hardest?

What would you have done differently?

What were some good ideas you saw that other groups came up with?

Extensions:

Have the students try a different course with different dimensions and slopes.